Contemporary biological research has suggested that some host-microbiome multispecies systems (referred to as "holobionts") can in certain circumstances evolve as unique biological individual, thus being a unit of selection in evolution. If this is so, then it is arguably the case that some biological adaptations have evolved at the level of the multispecies system, what we call hologenomic adaptations. However, no research has yet been devoted to investigating their nature, or how these adaptations can be distinguished from adaptations at the species-level (genomic adaptations). In this paper, we cover this gap by investigating the nature of hologenomic adaptations. By drawing on the case of the evolution of sanguivory diet in vampire bats, we argue that a trait constitutes a hologenomic adaptation when its evolution can only be explained if the holobiont is considered the biological individual that manifests this adaptation, while the bacterial taxa that bear the trait are only opportunistic beneficiaries of it. We then use the philosophical notions of emergence and inter-identity to explain the nature of this form of individuality and argue why it is special of holobionts. Overall, our paper illustrates how the use of philosophical concepts can illuminate scientific discussions, in the trend of what has recently been called metaphysics of biology.

Holobionts are symbiotic assemblages composed by a host plus its microbiome. The status of holobionts as individuals has recently been a subject of continuous controversy, which has given rise to two main positions: on the one hand, holobiont advocates argue that holobionts are biological individuals; on the other, holobiont detractors argue that they are just mere chimeras or ecological communities, but not individuals. Both parties in the dispute develop their arguments from the framework of the philosophy of biology, in terms of what it takes for a "conglomerate" to be considered an interesting individual from a biological point of view. However, the debates about holobiont individuality have important ontological implications that have remained vaguely explored from a metaphysical framework. The purpose of this paper is to cover that gap by presenting a metaphysical approach to holobionts individuality. Drawing upon a conception of natural selection that puts the focus on the transgenerational recurrence of the traits and that supports the thesis that holobionts are units of selection, we argue that holobionts bear emergent traits and exert downward powers over the entities that compose them. In this vein, we argue, a reasonable argument can be made for conceiving holobionts as emergent biological individuals.

RESUMENSe analiza crítica y reflexivamente los paradigmas en investigación desde la polémica cualitativa y cuantitativa y su relación con la evolución de la investigación en enfermería. De esta manera se presentan las diferencias entre los enfoques, se identifican los problemas de investigación en enfermería en el marco de los paradigmas; finalmente se plantean alternativas y reflexiones para potenciar la investigación en enfermeria. El supuesto que subyace a través del artículo es que el paradigma cualitativo no presenta mayor frecuencia de uso en investigaciones en enfermería, debido a la deficiencia en el conocimiento de dicho enfoque y la inadecuada inclusión de ambos enfoques en el proceso enseñanza/aprendizaje desde el diseño curricular; sin embargo, se categoriza en la importancia de ambos paradigmas dependiendo del objeto de investigación y la visión del investigador.Palabras claves: Investigación, enfermería, paradigmas, triangulación. ABSTRACTParadigms in research are critically and reflexively analyzed since a qualitative and quantitative polemic point of view, and their relationship with the evolution of the nursing research, likely the differences are presented, among the focuses, the investigation problems are identified in Nursing in the framework of the paradigms; finally alternatives and reflections regarding nursing research are presented. The supposition that underlies through the article is that the qualitative paradigm does not present bigger use frequency in nursing investigations, due to the deficiency in the knowledge of this focus and the inadequate inclusion of both focuses in the process teaching/learning from the curricular design; however, it is categorized in the importance of both paradigms depending on the investigation object and the investigator's vision. Keywords:Research, nursing, paradigms, triangulation. : 14.07.2004: 14.07. . Aceptación: 02.05.2005. Recepción INTRODUCCIÓNEl propósito en este trabajo es realizar análi-sis crítico y reflexivo de los paradigmas y su relación con la investigación en enfermería. Inicialmente se aborda conceptos y generalidades sobre paradigmas y antecedentes históricos de éstos. Luego se presentan las especificidades y diferencias de los enfoques positivista cuantitativo y del sustantivista cualitativo. Se continúa con la evolución histórica de la investigación en enfermería, los paradigmas y los problemas encontrados en la investigación de enfermería, en el marco de los paradigmas, alternativas y reflexiones para potenciar la investigación en enfermería. Finalmente se presentan las conclusiones.

The notion of fitness is usually equated to reproductive success. However, this actualist approach presents some difficulties, mainly the explanatory circularity problem, which have lead philosophers of biology to offer alternative definitions in which fitness and reproductive success are distinguished. In this paper, we argue  that none of these alternatives is satisfactory and, inspired by Mumford and Anjum's dispositional theory of causation, we offer a definition of fitness as a causal dispositional property. We argue that, under this framework, the distinctiveness that biologists usually attribute to fitness-namely, the fact that fitness is something different from both the physical traits of an organism and the number of offspring it leaves-can be explained, and the main problems associated with the concept of fitness can be solved. Firstly, we introduce Mumford and Anjum's dispositional theory of causation and present our definition of fitness as a causal disposition. We explain in detail each of the elements involved in our definition, namely: the relationship between fitness and the functional dispositions that compose it, the emergent character of fitness, and the context-sensitivity of fitness. Finally, we explain how fitness and realized fitness, as well as expected and realized fitness are distinguished in our approach to fitness as a causal disposition.

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